1. Field of the Invention
The present invention relates to a developing device of a wet type printer, and more particularly, to a developing device of a wet type printer in which the efficiency of cleaning a developing roller and the recovery rate of developer particles are enhanced.
2. Description of the Related Art
In general, an electrographic printer such as a laser printer uses a photosensitive medium such as a photosensitive belt on which a latent electrostatic image is formed. The electrographic printers are classified into two major groups, i.e., wet type printers and dry type printers according to the type of developer used. The wet type printers use a developer composed of a mixture of a volatile liquid carrier and a toner. The wet type electrographic printers using such a liquid developer exhibit better print quality than dry type electrographic printers which use powder toner. Further, the wet type printers prevent suffering from hazardous toner dust and are, therefore, being increasingly used.
Referring to FIG. 1, a photosensitive belt 110 circulates in a closed loop around three rollers 121, 122 and 123. The first roller 121 transfers a toner image formed on the photosensitive belt 110 to a transfer roller 124. The transfer roller 124 then transfers the transferred toner image to a paper 125. A pressing roller 128, which contacts the transfer roller 124 with the paper 125 therebetween, presses the paper 125 toward the transfer roller 124 at a constant pressure to transfer the toner image on the transfer roller 124 to the paper 125. A charging device 135, for charging the photosensitive surface of the photosensitive belt 110, is positioned along the path of the photosensitive belt 110 between the first roller 121 and the second roller 122. Laser scanning units 130 form a latent electrostatic image by illuminating a laser beam on the photosensitive surface of the photosensitive belt 110. Developing devices 140 of respective colors develop the latent electrostatic image into the toner image by supplying the scanned photosensitive surface with developer liquid. The laser scanning units 130 and the developing devices are alternately installed along the path of the photosensitive belt 110 between the second roller 122 and the third roller 123. Pairs of backup rollers 126 and 127, corresponding to the respective developing devices 140, are installed inside the photosensitive belt 110 between the second roller 122 and the third roller 123.
Referring to FIG. 2, the conventional developing device 140 is provided with a first squeegee roller 146 and a developing roller 143 corresponding to the backup rollers 126 and 127. A cleaning roller 144 which rotates in the same direction as the developing roller 143, is installed at a lower part of the developing roller 143. A lower portion of the cleaning roller 144 is immersed in developer liquid 141. A second squeegee roller 147 is installed alongside of the first squeegee roller 146. The squeegee rollers 146 and 147 squeegee the developer liquid adhering to the photosensitive belt 110. Scrapers 146a and 147a remove developer liquid from squeegee rollers 146 and 147, respectively. A developer liquid supplying device 148 is installed alongside of the developing roller 143. A blade 149 installed between the developer liquid supplying device 148 and the developing roller 143 for preventing the developer liquid supplied from the developer liquid supplying device 148 from flowing in a direction opposite that of the rotation of the developing roller 143.
As shown in FIGS. 3 and 4, the tubular rotating shaft 200 of the cleaning roller 144 is provided with developer liquid passages 232 on the circumferential surface thereof. A plurality of cleaning members 201 are closely fitted on the circumferential surface of the tubular rotating shaft. Since the cleaning roller 144 rotates in the same direction as does the developing roller 143, there is friction between the cleaning members 201 and the developing roller 143 thereby cleaning the surface of the developing roller 143. Developing liquid for cleaning developing roller 143 is supplied through a cavity 202 of the tubular rotating shaft 200.
In the conventional developing device as described above, the structure of the cleaning device for cleaning the developing roller 143 is complicated. In addition, when the cleaning members are partially abraded, some particles of the developer liquid remain adhered to the developing roller 143. The remaining particles are separated from the developing roller 143 by the blade 149. The removed particles may adhere to the developer liquid supplying device in a sludge state, and accordingly recovery of particles for reuse is not effectively accomplished. Further, because the developing roller and the cleaning roller are driven by separate motors and the relative frictional force is relatively large, more powerful motors are required.